The INS Arihant, India’s first nuclear-powered submarine armed with ballistic missiles (SSBN, in military jargon)… is a 6,000-tonne boat that will provide India with the third leg of its nuclear “triad”—it already has land- and air-launched nukes….India believes SSBNs are a vital part of its nuclear strategy, which forswears the first use of nuclear weapons….Because they can readily avoid detection, SSBNs can survive a surprise attack and thus ensure India’s ability to launch a retaliatory “second strike”….Some nuclear theorists argue that submarine-based deterrents promote peace by making the other side more frightened to attack first. …
China is ahead of the game. It has a fleet of four second-generation Jin-class SSBNs and is testing JL-2 missiles to install in them. These weapons have a range of 7,400km (4,600 miles)—too short, for now, to reach the American mainland from the relative safety of the South China Sea. Pakistan, for its part, is in the early stages of a lower-cost approach. This involves arming diesel-powered subs with nuclear-armed cruise missiles with a range of 700km.
A more immediate worry to India is Pakistan’s development and deployment of smaller “tactical” nuclear weapons for use on the battlefield. These may make it more likely that any war between India and Pakistan will go nuclear. They also increase the risk of Pakistan’s weapons being used accidentally—or falling into the hands of extremists (such weapons are under the control of lower-level commanders whose professionalism and loyalty may be dubious)….
India says it will not develop battlefield nukes of its own. Instead, it will rely on the threat of massive retaliation against any use of nuclear weapons by Pakistan. Still, it may be another decade before India has a fully-fledged sea-based deterrent. Arihant’s Russian nuclear-power generator is unsuited to long patrols. Initially, the sub is due to be armed with the K-15 missile, with a range of 750km—not enough to reach big cities in northern Pakistan. Striking Chinese ones would be harder still.
Asian Nuclear Weapons: What Lurks Beneathh, Economist, Feb. 6, 2016, at 36